The invention is the use of terminally blocked polyethylene-glycol ethers as foam suppressing additives in low-foam cleaning agents. The invention makes available foam suppressing agents which combine high effectiveness with low toxicity and biodegradability. The agents of the invention are suitable for effectively suppressing foam formation in cleaning processes such as spray cleaning, in the low temperature range, particularly in the range of ambient temperature.
Aqueous cleaning agents intended for use in industry, in particular those for cleaning metal, glass, and ceramic surfaces, usually contain substances which are capable of counteracting formation of foam. The use of foam-suppressing additives is required because the impurities which are loosened from the substrates and which collect in the cleaning baths act as foaming agents. In addition, the use of foam suppressing agents may also be necessary because the cleaning agent themselves contain constituents, which form foam, under the prescribed operating conditions. As an example, the anionic tensides which are used to a great extent in cleaning agents tend to produce foam.
2. State of Related Art
Addition products of alkylene oxides to organic compounds with reactive hydrogen atoms in the molecule have been used as foam reducing agents. Addition products of propylene oxide to aliphatic polyalcohols--see the example DE-PS 1 280 455 and DE-PS 1 621 592--and in aliphatic polyamines--cf. for example DE-PS 1 289 597 and DE-PS 1 621 593--as well as addition products of ethyleneoxide and propyleneoxide to aliphatic polyamines, particularly ethylenediame--cf. DE-PS 1 944 569 have in particular proved useful in practice. These alkylene oxide addition products, possess in addition to good foam reducing properties, the alkali stability generally required for use in commercial and industrial cleaning compositions. The compounds of this class are however not sufficiently biodegradable to satisfy current legal regulations.
A class of highly effective and at the same time biodegradable antifoam agents is described in DE-OS 33 15 951. The use of terminally blocked polyethylene glycol ethers of the formula (1) R.sub.1 O--(CH.sub.2 CH.sub.2 O).sub.n --R.sub.2 is described, wherein R.sub.1 is a straight-chain or branched alkyl or alkenyl radical with from 8 to 18 carbon atoms, R.sub.2 is an alkyl radical with from 4 to 8 carbon atoms and n is an integer of from 7 to 12. In practice a composition which has proven particularly useful is a compound in which R.sub.1 is a fatty alcohol radical with from 12 to 18 carbon atoms, R.sub.2 is an n-butyl radical, and n is 10.
The present invention is based on the unexpected discovery that varying the terminal end-group fatty alcohol, polyethylene glycol ether structures provides more effective foam-suppressing agents. With the method according to the invention, it is possible to increase the effectiveness while retaining the low toxicity and biodegradability of the foam suppressing additives. The ethylene glycol ethers of the present invention provide improved effectiveness in the low temperature range, for example in the ambient temperature range or at slightly higher temperatures.
The discovery is unexpected in comparison with previously known anti-foam agents. It is known, that in commercial cleaning processes rinsing processes are frequently carried out at low temperatures, in order, to carry out energy-saving precleaning. Conventional foam-suppressing additives generally suppress foam effectively in a temperature range above about 50.degree. C. , however, their use at a temperature of about 20.degree. C. provides a comparatively weaker foam-suppressing effect. Unexpectedly the additives according to the invention are particularly effective at low temperatures and suppress foam when they are blended with previously used components of similar structure.